This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. A prophylactic vaccine is much needed for controlling the HIV/AIDS pandemics, and a potential vaccine platform can comprise of an HIV-1 envelope gp120 antigen/antibody complex made with a selected anti-gp120 monoclonal antibody (mAb) that upon binding to the antigen augments the antigenicity and immunogenicity of a neutralizing epitope of interest. When forming these complexes, multiple species of different sizes (determined by size exclusion chromatography) with unknown stoichiometry can be isolated. SAXS may provide necessary information in understanding the immunogen complex formation, hence guiding the vaccine discovery.